No, I'm not going to ask how much lift I need.
What I would like to know is - if you are properly weighted to be neutral with 500 psi at 15 feet why do you need more than nominal lift. As you rise from 15 feet to the surface you should become slightly positively buoyant, so why the need for more than a few pounds of lift?
@cool_hardware52 has explained this in depth several times and we have a slight difference of opinion on the last point I'll make which stems mainly from his side of the woods with thick wetsuits and drysuits.
Point 1-your wing needs to compensate for the mass of the gas in your tank
Point 2-your wing needs to compensate for the compression of your wetsuit
Point 3-your wing needs to be able to float your entire rig at the surface. More lift required if you put all of your ballast in pockets, less if you wear a weight belt
Point 4-your wing needs to be able to float you, in your entire rig, comfortably at the surface
Now, the difference of opinion that Tobin and I have is how much extra lift you need for point 4. If you are balanced at 15ft in a thick wetsuit, there is a good bit of compression that goes on that is often enough to keep your head above water. I weight myself for neutral at the surface since I teach and always need to be able to comfortably go down and I often dive in thin/no exposure protection. I need to be able to comfortably stay at the surface at the beginning of the dive and that means more lift than the minimum.
So for me in normal single tank diving
LP121- 12ish lbs of gas
3mm wetsuit-6lbs ish of compression
6lbs of lead in the ocean to be neutral, usually on a weight belt
15lbs of my head.
I don't own or dive with less than 30lb wings personally because of that. If I regularly dove AL80's in no exposure protection, I'd consider a smaller wing, but the difference in drag between my LCD30 from Deep Sea Supply and my VDH 35lb wing is negligible since they are long and narrow wings.